Cooling system and vehicle with the same

ABSTRACT

A cooling system for cooling a heat source includes a flow channel through which liquid medium cooling the heat source is circulated, and a pump provided on the flow channel for circulating the liquid medium. The flow channel includes a plurality of branches arranged between an upstream side and a downstream side of the heat source in parallel to a distribution direction of the liquid medium. The cooling system further includes a control device for detecting an abnormality occurred in the cooling system by detecting an imbalance among flow rates of the liquid medium flowing through the plurality of branches, respectively.

TECHNICAL FIELD

The present invention relates to a cooling system and a vehicle with the same, and more particularly relates to a technique for diagnosing a partial abnormality of the cooling system.

BACKGROUND ART

In order to prevent a motor and a driving device, such as an inverter, driving the motor from overheating, an electric powered vehicle with the motor used as a drive source is equipped with a cooling system for cooling the motor and the driving device.

Japanese Patent Laying-Open No. 2008-256313 (PTD 1) discloses a cooling system equipped with a circulation channel for cooling water, a pump circulating the cooling water through the circulation channel and a radiator cooling the cooling water.

A control device of the cooling system described in PTD 1 includes, as a technique for determining the presence/absence of occurrence of abnormality of the cooling system, an abnormality determination unit determining the type of abnormality occurring in the cooling system based on the temperature of cooling water acquired from a temperature sensor provided for the circulation channel for cooling water and the speed of the water pump. When the cooling water has a temperature more than or equal to a threshold value set previously, this abnormality determination unit determines the type of abnormality, such as an abnormality of the radiator, clogging of the circulation channel and a malfunction of the water pump, based on the speed of the water pump.

Citation List Patent Document PTD 1: Japanese Patent Laying-Open No. 2008-256313 PTD 2: Japanese Patent Laying-Open No. 2005-20881 PTD 3: Japanese Patent Laying-Open No. 2004-332988 SUMMARY OF INVENTION Technical Problem

With the technique for determining the presence/absence of occurrence of abnormality in a cooling system based on the temperature of cooling water and the speed of a water pump as described in PTD 1, the type of abnormality occurred in the cooling system can be determined. However, it is difficult to determine the cause of the abnormality. Therefore, with the technique described in PTD 1, fail-safe processing, such as restricting motor's output torque or stopping the water pump can be performed depending on the type of abnormality, however, processing for removing the cause of the abnormality cannot be performed.

The present invention was therefore made to solve such a problem, and has an object to provide a cooling system capable of identifying the cause of an abnormality occurred in the cooling system and removing the cause of the abnormality, as well as a vehicle equipped with such cooling system.

Solution to Problem

According to an aspect of the present invention, a cooling system for cooling a heat source includes a flow channel through which liquid medium cooling the heat source is circulated, and a pump provided on the flow channel for circulating the liquid medium. The flow channel includes a plurality of branches arranged between an upstream side and a downstream side of the heat source in parallel to a distribution direction of the liquid medium. The cooling system further includes a control device for detecting an abnormality occurred in the cooling system by detecting an imbalance among flow rates of the liquid medium flowing through the plurality of branches, respectively.

Preferably, the control device diagnoses a cause of occurrence of the abnormality at least based on the speed of the pump when the imbalance among the flow rates of the liquid medium is detected.

Preferably, the cooling system further includes a speed sensor for detecting the speed of the pump. In the case where the imbalance among the flow rates of the liquid medium is detected, the control device diagnoses that air has entered the flow channel when a first condition that a detection value of the speed sensor obtained when the pump is driven is higher than a control target value is met.

Preferably, the cooling system further includes a temperature sensor for detecting the temperature of the liquid medium. In the case where the first condition is not met, the control device determines whether or not a second condition that a detection value of the temperature sensor is lower than a predetermined threshold value is met, and when the second condition is met, the control device diagnoses that the flow channel is frozen.

Preferably, in the case where the second condition is met, the control device determines whether or not a flow rate of the flow channel falls within a control range, and when a third condition that the flow rate of the flow channel falls within the control range is met, the control device diagnoses that any of the plurality of branches is frozen.

Preferably, in the case where the first condition is not met, the control device diagnoses that a foreign substance has entered any of the plurality of branches when the second condition is not met.

Preferably, in the case where it is diagnosed that one of air and a foreign substance has entered any of the plurality of branches, the control device temporarily increases the speed of the pump.

Preferably, in the case where it is diagnosed that any of the plurality of branches is frozen, the control device temporarily increases the amount of heat generation of a heat source corresponding to a branch diagnosed as frozen.

Preferably, the heat source is a driving device having a motor and an inverter driving the motor. The cooling system further includes an element temperature sensor detecting the temperature of a power control element in the inverter. Under a situation where a condition that another driving instruction is not issued to the inverter is satisfied, the control device temporarily causes the power control element in the inverter to generate heat and then reduces heat generation of the power control element to presume the flow rates of the plurality of branches depending on the degree of drop of a detection value of the element temperature sensor, and detects an imbalance among the flow rates of the liquid medium based on presumed values of the flow rates of the plurality of branches.

Preferably, the plurality of branches are configured to have an equal flow rate.

According to another aspect of the present invention, a vehicle includes a driving device using a motor as a drive source, and a cooling system for cooling the driving device. The cooling system includes a flow channel through which liquid medium cooling the driving device is circulated, and a pump provided on the flow channel for circulating the liquid medium. The flow channel includes a plurality of branches arranged between an upstream side and a downstream side of the heat source in parallel to a distribution direction of the liquid medium and configured to have an equal flow rate. The vehicle further includes a control device for detecting an abnormality occurred in the cooling system by detecting an imbalance among flow rates of the liquid medium flowing through the plurality of branches, respectively.

Advantageous Effects of Invention

According to the present invention, when an abnormality occurred in the cooling system is detected, the cause of the abnormality can be identified, and the cause of the abnormality can be removed. Thereby, even if an abnormality occurs in the cooling system, abnormality determination can be prevented from being immediately finalized. As a result, a restriction on the output of the driving device or unnecessary exchange of water pumps can be avoided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of a vehicle equipped with a cooling system according to an embodiment of the present invention.

FIG. 2 is a diagram showing the configuration of the cooling system taken out from the configuration of the vehicle of FIG. 1.

FIG. 3 is a conceptual view illustrating the configuration of flow channel passing through PCU.

FIG. 4 is a flowchart schematically showing a processing structure of a control device.

FIG. 5 is a flowchart for achieving cause-of-abnormality removal control shown in step S04 of FIG. 4.

FIG. 6 is a waveform diagram for illustrating diagnostic timing of a cooling system according to the present exemplary modification.

FIG. 7 is a flowchart for illustrating control of diagnostic timing of the cooling system shown in FIG. 6.

FIG. 8 is a flowchart for illustrating flow-rate detection processing used in diagnosing the cooling system in step S20 of FIG. 7.

FIG. 9 is a diagram showing an example of water temperature-command torque map referred to in step S23 of FIG. 8.

FIG. 10 is a diagram for illustrating measurements of temperature drop rate.

FIG. 11 is a diagram showing an example of drop rate-flow rate map.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It is noted that, in the drawings, the same or corresponding portions have the same reference characters allotted, and repeated description thereof will not be provided.

Vehicular Configuration

FIG. 1 is a schematic configuration diagram of a vehicle 100 equipped with a cooling system according to an embodiment of the present invention. It is noted that, although vehicle 100 is shown as an electric vehicle by way of example, the present invention is applicable not only to an electric vehicle but also to any hybrid vehicle with an internal combustion engine used in combination or any fuel-cell vehicle that is equipped with a cooling system.

Referring to FIG. 1, vehicle 100 includes a battery B as a power storage device, a voltage sensor 10, a power control unit (PCU) 40, a motor-generator MG, and a control device 30. PCU 40 includes a voltage converter 12, smoothing capacitors C0 and C1, a voltage sensor 13, and an inverter 14. It is noted that PCU 40 may include inverter 14 alone, without being provided with voltage converter 12. Vehicle 100 further includes a positive bus PL2 for supplying electric power to inverter 14 driving motor-generator MG.

Smoothing capacitor C1 is connected across positive bus PL1 and a negative bus SL2. Voltage converter 12 boosts a voltage across the terminals of smoothing capacitor C1. Smoothing capacitor C0 smoothes the voltage boosted by voltage converter 12. Voltage sensor 13 detects a voltage VH across the terminals of smoothing capacitor C0, and outputs the voltage to control device 30.

Vehicle 100 further includes a system main relay SMRB connected across a positive electrode of battery B and positive bus PL1 and a system main relay SMRG connected across a negative electrode of battery B (negative bus SL1) and a node N2.

The conducting/non-conducting state of system main relays SMRB and SMRG is controlled in response to a control signal SE supplied from control device 30. Voltage sensor 10 detects a voltage VB across the terminals of battery B. Although not shown, in order to monitor the state of charge of battery B, a current sensor for detecting a current IB flowing through battery B is provided together with voltage sensor 10.

Battery B can be implemented by, for example, a secondary battery such as a lead acid battery, a nickel-metal hydride battery or a lithium ion battery, or a large-capacitance capacitor such as an electric double layer capacitor, or the like. Negative bus SL2 extends to the inverter 14 side passing through voltage converter 12.

Voltage converter 12 is a voltage converter provided across battery B and positive bus PL2 and performing voltage conversion. Voltage converter 12 includes a reactor L1 having one end connected to positive bus PL1, IGBT elements Q1 and Q2 connected in series across positive bus PL2 and negative bus SL2, and diodes D1 and D2 connected to IGBT elements Q1 and Q2, respectively.

Reactor L1 has its other end connected to the emitter of IGBT element Q1 and the collector of IGBT element Q2. Diode D1 has its cathode connected to the collector of IGBT element Q1, and diode D1 has its anode connected to the emitter of IGBT element Q1. Diode D2 has its cathode connected to the collector of IGBT element Q2, and diode D2 has its anode connected to the emitter of IGBT element Q2.

Inverter 14 is connected to positive bus PL2 and negative bus SL2. Inverter 14 converts a DC voltage output from voltage converter 12 into a three-phase AC voltage for output to motor-generator MG that drives a wheel 2. Also, inverter 14 returns electric power generated in motor-generator MG to voltage converter 12 following regenerative braking. At this time, voltage converter 12 is controlled by control device 30 to operate as a step-down circuit.

Inverter 14 includes a U-phase arm 15, a V-phase arm 16 and a W-phase arm 17. U-phase arm 15, V-phase arm 16 and W-phase arm 17 are connected in parallel across positive bus PL2 and negative bus SL2.

U-phase arm 15 includes IGBT elements Q3 and Q4 connected in series across positive bus PL2 and negative bus SL2 and diodes D3 and D4 connected in parallel to IGBT elements Q3 and Q4, respectively. Diode D3 has its cathode connected to the collector of IGBT element Q3, and diode D3 has its anode connected to the emitter of

IGBT element Q3. Diode D4 has its cathode connected to the collector of IGBT element Q4, and diode D4 has its anode connected to the emitter of IGBT element Q4.

V-phase arm 16 includes IGBT elements Q5 and Q6 connected in series across positive bus PL2 and negative bus SL2 and diodes D5 and D6 connected in parallel to IGBT elements Q5 and Q6, respectively. Diode D5 has its cathode connected to the collector of IGBT element Q5, and diode D5 has its anode connected to the emitter of IGBT element Q5. Diode D6 has its cathode connected to the collector of IGBT element Q6, and diode D6 has its anode connected to the emitter of IGBT element Q6.

W-phase arm 17 includes IGBT elements Q7 and Q8 connected in series across positive bus PL2 and negative bus SL2 and diodes D7 and D8 connected in parallel to

IGBT elements Q7 and Q8, respectively. Diode D7 has its cathode connected to the collector of IGBT element Q7, and diode D7 has its anode connected to the emitter of IGBT element Q7. Diode D8 has its cathode connected to the collector of IGBT element Q8, and diode D8 has its anode connected to the emitter of IGBT element Q8.

Motor-generator MG is a three-phase permanent magnet synchronous motor, and three stator coils of U, V and W phases have their one ends connected in common to a neutral point. The U-phase coil has its other end connected to a line drawn from a connection node between IGBT elements Q3 and Q4. The V-phase coil has its other end connected to a line drawn from a connection node between IGBT elements Q5 and Q6. The W-phase coil has its other end connected to a line drawn from a connection node between IGBT elements Q7 and Q8.

A current sensor 24 detects a current flowing in motor-generator MG as a motor current MCRT, and outputs motor current MCRT to control device 30. Control device 30 receives an accelerator pedal position from an accelerator sensor 111, and receives a set position of a shift lever from a shift position sensor 113. Furthermore, control device 30 receives a rotation speed (motor speed) Nm of motor-generator MG, respective values of current IB and voltages VB, VH, motor current MCRT, and an activation signal IGON. Control device 30 then controls voltage converter 12 and inverter 14 based on these pieces of information.

More specifically, control device 30 outputs, to voltage converter 12, a control signal PWU giving a boost instruction, a control signal PWD giving a step-down instruction and a shutdown signal instructing prohibition of movement.

Control device 30 also outputs, to inverter 14, a control signal PWMI giving a driving instruction of converting a DC voltage output from voltage converter 12 into an

AC voltage for driving motor-generator MG and a control signal PWMC giving a regeneration instruction of converting an AC voltage generated by motor-generator MG into a DC voltage for return to the voltage-converter 12 side.

Configuration of Cooling System

In the configuration shown in FIG. 1, vehicle 100 further includes a radiator 102, a reservoir tank 106 and a water pump 104, as a cooling system for cooling PCU 40 and motor-generator MG. FIG. 2 shows the configuration of the cooling system taken out from the configuration of vehicle 100 of FIG. 1.

Radiator 102, PCU 40, reservoir tank 106, water pump 104, and motor-generator MG are circularly connected in series by a flow channel 116.

Water pump 104 is a pump for circulating cooling water such as an antifreeze solution. Water pump 104 pumps up cooling water from reservoir tank 106, and circulates cooling water toward motor-generator MG. A speed sensor 114 detects a rotation speed (hereinafter denoted as W/P speed) NW of water pump 104, and outputs detected W/P speed NW to control device 30.

Radiator 102 receives cooling water having cooled voltage converter 12 and inverter 14 within PCU 40 from flow channel 116, and cools the received cooling water using a radiator fan not shown.

A temperature sensor 108 detecting the temperature of cooling water is provided in proximity to a cooling water inlet of PCU 40. A cooling water temperature TW is transmitted from temperature sensor 108 to control device 30. Moreover, a temperature sensor 110 detecting a temperature TC of voltage converter 12 and a temperature sensor 112 detecting a temperature TI of inverter 14 are provided within PCU 40. Temperature sensors 110 and 112 are implemented by temperature detecting elements, for example, built in an intelligent power module.

Control device 30 generates a signal SP for driving water pump 104 based on temperature TC from temperature sensor 110 and temperature TI from temperature sensor 112, and outputs generated signal SP to water pump 104.

In the configuration shown in FIG. 2, flow channel 116 in a zone from the upstream side to the downstream side of PCU 40 is branched into a plurality of branches. FIG. 3 is a conceptual view illustrating the configuration of flow channel 116 passing through PCU 40. Referring to FIG. 3, provided within PCU 40 is a power element substrate 400 on which power control elements (IGBT elements etc.) of voltage converter 12 and inverter 14 are mounted. A flow channel 122 for cooling power element substrate 400 is provided on the rear surface of this power element substrate 400. Flow channel 122 communicates with a cooling water inlet 120 and a cooling water outlet 124.

In FIG. 3, the plurality of power control elements mounted on power element substrate 400 are divided into three element sections (element sections 1 to 3). Flow channel 122 is branched into three branches B1 to B3 to pass through these three element sections, respectively. These three branches B1 to B3 are arranged between cooling water inlet 120 and cooling water outlet 124 in parallel to the distribution direction of cooling water, and are configured such that their flow rates are equal to one another. Therefore, cooling water introduced through cooling water inlet 120 is trisected, and then flows through branches B1 to B3 in the direction indicated by arrows P1 to P3, respectively. At this time, the cooling water flowing through each branch and each element section exchange heat with each other, so that the power control elements included in the element sections are cooled.

Flow sensors 131 to 133 for detecting the flow rate of cooling water are provided for branches B1 to B3, respectively. From flow sensor 131, a flow rate Fa of cooling water in branch B1 is transmitted to control device 30. From flow sensor 132, a flow rate Fb of cooling water in branch B2 is transmitted to control device 30. From flow sensor 133, a flow rate Fc of cooling water in branch B3 is transmitted to control device 30.

Control device 30 diagnoses a partial abnormality of the cooling system based on flow rates Fa, Fb and Fc input from flow sensors 131 to 133, respectively. The partial abnormality of the cooling system as used in the present embodiment refers to the occurrence of an abnormality in any of the plurality of branches. FIG. 3 shows the case where a foreign substance has entered branch B1 as an example of partial abnormality. In this case, the flow rate of cooling water flowing through branch B1 decreases, so that an imbalance in flow rate among branches B1 to B3 occurs. When such an imbalance in flow rate occurs, a difference in cooling capacity occurs among element sections 1 to 3, which may cause a problem in that the element temperature partly becomes higher. In the case of FIG. 3, an element temperature T1 of element section 1 may become higher than an element temperature T2 of element section 2 and an element temperature T3 of element section 3. It is therefore necessary to quickly detect a partial abnormality of the cooling system and to solve an imbalance in flow rate due to the partial abnormality.

In the cooling system according to the present embodiment, control device 30 detects whether an imbalance among flow rates Fa, Fb and Fc has occurred based on detection values (flow rates Fa, Fb and Fc) of flow sensors 131 to 133 in accordance with FIGS. 4 and 5 which will be described below. When an imbalance among flow rates has occurred, control device 30 determines it as a partial abnormality of the cooling system.

Then, when the partial abnormality of the cooling system is determined, control device 30 diagnoses the cause of the partial abnormality based on the condition of the cooling system when the partial abnormality has occurred. When the cause of the partial abnormality is diagnosed, control device 30 further executes control for removing the diagnosed cause to thereby solve the partial abnormality.

FIG. 4 is a flowchart schematically showing a processing structure of control device 30. It is noted that the processing of this flowchart is executed at regular time intervals or every time predetermined conditions are met.

Referring to FIG. 4, control device 30 in step S01 reads flow rates Fa, Fb and Fc of branches B1 to B3 detected by flow sensors 131 to 133 (FIG. 3), respectively. Next, control device 30 in step S02 monitors rotation speed (W/P speed) NW of water pump 104 detected by speed sensor 114 (FIG. 1). Control device 30 in step S03 determines whether a partial abnormality of the cooling system has occurred based on flow rates Fa, Fb and Fc. More specifically, control device 30 determines whether or not an imbalance among flow rates Fa, Fb and Fc has occurred. For example, control device 30 calculates the ratio of each of flow rates Fa, Fb and Fc relative to the total value of flow rates Fa, Fb and Fc (equivalent to a flow rate Ft of flow channel 116). Control device 30 then compares the calculated ratios to thereby determine whether or not an imbalance among the flow rates has occurred.

When the calculated ratios differ among flow rates Fa, Fb and Fc, that is, when the ratio of each flow rate deviates from one third, control device 30 determines that a partial abnormality of the cooling system has occurred. At this time, control device 30 determines that an abnormality has occurred in a branch having a smaller ratio of flow rate than the other branches.

When it is determined in step S03 that a partial abnormality of the cooling system has occurred, control device 30 in step S04 diagnoses the cause of the partial abnormality based on the condition of the cooling system when the partial abnormality has occurred. Then, control device 30 executes control for removing the diagnosed cause (hereinafter referred to as “cause-of-abnormality removal control”). When the partial abnormality is not solved by execution of the cause-of-abnormality removal control, control device 30 in step S05 finalizes the abnormality of the cooling system.

When the abnormality of the cooling system is finalized, control device 30 causes a warning to be displayed on a display device, a warning lamp or the like.

FIG. 5 is a flowchart for achieving the cause-of-abnormality removal control shown in step S04 of FIG. 4. It is noted that the processing in steps S01 and S02 of FIG. 5 is the same as the processing in steps S01 and S02 of FIG. 4. The processing in steps S031, S032 and S033 of FIG. 5 corresponds to the processing in step S03 of FIG. 4.

Referring to FIG. 5, control device 30 in step S01 reads flow rates Fa, Fb and Fc of branches B1 to B3 detected by flow sensors 131 to 133 (FIG. 3), respectively, and in step S02 monitors rotation speed (W/P speed) NW of water pump 104. Control device 30 in step S031 determines whether or not an imbalance among flow rates Fa, Fb and Fc has occurred based on the result of comparison among the ratios of respective flow rates Fa, Fb and Fc relative to flow rate Ft of flow channel 116. When an imbalance among flow rates Fa, Fb and Fc has not occurred (when determined NO in step S031), control device 30 in step S033 determines the cooling system as being normal.

On the other hand, when an imbalance among flow rates Fa, Fb and Fc has occurred (when determined YES in step S031), control device 30 in step S032 determines that a partial abnormality of the cooling system has occurred. Control device 30 determines that the partial abnormality has occurred in a branch of plurality of branches B1 to B3 that has a smaller ratio of flow rate relative to flow rate Ft. When it is determined in step S032 that a partial abnormality of the cooling system has occurred, control device 30 performs processing in steps S041 to S050, thereby diagnosing the cause of the partial abnormality and executing the cause-of-abnormality removal control for the cooling system.

More specifically, first, control device 30 in step S041 determines whether or not W/P speed NW has increased based on monitored W/P speed NW. When W/P speed NW has increased (when determined YES in step S041), control device 30 in step S045 diagnoses that air may have entered the branch determined as being abnormal. Air entering a branch means that a mass of air exists in that branch.

When air has entered the flow channel, the load imposed on water pump 104 becomes smaller than in the case where air has not entered. The real speed of water pump 104 thus becomes higher than a control speed specified by signal SP. When the state that W/P speed NW is higher than the control speed is continued for a predetermined time or longer, control device 30 diagnoses that air may have entered the branch.

When it is diagnosed in step S045 that air may have entered the branch, control device 30 in step S044 temporarily increases the output of water pump 104. For example, control device 30 drives water pump 104 at the maximum speed for a certain time period. When the discharge flow rate of water pump 104 increases by the increase in the speed of water pump 104, air existing in the branch is forced to flow into reservoir tank 106 together with cooling water. In reservoir tank 106, air is isolated from the cooling water, and is discharged to the atmosphere. Air existing in the branch can thereby be removed.

In contrast, when W/P speed NW has not increased in step S041 (when determined NO in step S041), control device 30 in step S042 determines whether or not cooling water temperature TW detected by temperature sensor 108 is less than or equal to a predetermined threshold value. The predetermined threshold value is set at a temperature at which the cooling water in the flow channel becomes frozen, for example. It is noted that a determination may be made based on a detection value of a temperature sensor for detecting the outside air temperature, instead of cooling water temperature TW detected by temperature sensor 108.

When cooling water temperature TW is less than or equal to the predetermined threshold value (when determined YES in step S042), control device 30 then in step S046 determines whether or not flow rate Ft of cooling water flowing through flow channel 116 is normal. Control device 30 calculates, as flow rate Ft, the total value of flow rates Fa, Fb and Fc detected by flow sensors 131 to 133, respectively. When flow rate Ft falls within a flow rate control range in accordance with the control speed of water pump 104, control device 30 determines flow rate Ft as being normal.

When flow rate Ft is determined in step S046 as being normal (when determined YES in step S046), control device 30 in step S047 diagnoses that branches B1 to B3 shown in FIG. 3 may be partly frozen because the cooling water temperature is low. Control device 30 presumes that a branch of plurality of branches B1 to B3 that has a smaller ratio of flow rate relative to the total flow rate than the other branches is frozen. Then, control device 30 in step S048 forces an element section corresponding to that branch presumed to be frozen to generate heat. More specifically, control device 30 outputs a control signal for bringing about the conducting state for a short time, to a power control element included in the element section corresponding to that branch. It is noted that, since this control signal is intended to cause a power control element to generate heat, it is not to produce torque for driving the vehicle like control signals PWMI and PMWC. By the self-heating of the power control element for a short time, the branch can be defreezed.

In contrast, when flow rate Ft is determined in step S046 as not being normal (when determined NO in step S046), control device 30 in step S049 diagnoses that flow channel 116 including plurality of branches B1 to B3 may be frozen. In this case, control device 30 in step S050 forces all element sections 1 to 3 to generate heat. More specifically, control device 30 outputs a control signal for bringing about the conducting state for a short time to power control elements included in element sections 1 to 3. By the self-heating of all the power control elements mounted on power element substrate 400 for a short time, the flow channel can be defreezed.

Returning to step S042, when cooling water temperature TW is not less than or equal to the predetermined threshold value (when determined NO in step S042), control device 30 diagnoses that a foreign substance or air may have entered part of plurality of branches B1 to B3. Control device 30 presumes that a foreign substance or air has entered a branch of plurality of branches B1 to B3 that has a smaller ratio of flow rate relative to the total flow rate. It is noted that entrance of air into a branch in step S043 means that a mass of air exists in that branch similarly to step S045. However, step S043 is different in that a case is presumed in which the flow area of that branch is smaller because of the presence of numerous masses of air of smaller size in the branch than in step S045.

When it is diagnosed in step S041 that a foreign substance or air may have entered the branch, control device 30 in step S044 temporarily increases the output of water pump 104. By increasing the discharge flow rate of water pump 104 as described above, the foreign substance or air existing in the branch can be removed.

As described above, when the cause of the partial abnormality of the cooling system is diagnosed based on the speed of water pump 104 and the cooling water temperature, the cause-of-abnormality removal control is executed in an optimum control mode for removing the diagnosed cause. Then, control device 30 in step S051 determines whether or not the imbalance among flow rates Fa, Fb and Fc has been solved. When the imbalance among the flow rates has not been solved (when determined NO in step S051), control device 30 in step S05 finalizes the abnormality of the cooling system.

On the other hand, when the imbalance among the flow rates has been solved by the above-described cause-of-abnormality removal control (when determined YES in step S051), control device 30 in step S06 determines that the partial abnormality of the cooling system has been solved and the cooling system has been returned to the normal state.

As described above, the cooling system according to the present embodiment can detect the partial abnormality of the cooling system by determining whether or not an imbalance in flow rate of cooling water has occurred among the plurality of branches connected in parallel to the distribution direction of cooling water.

Here, as described above, when an imbalance in flow rate of cooling water has occurred among the plurality of branches, a problem may arise in that the element temperature becomes partly higher. Therefore, it can be configured such that an abnormality of the cooling system is determined based on detection values of temperature sensor 110 detecting temperature TC of voltage converter 12 and temperature sensor 112 detecting temperature TI of inverter 14 (see FIG. 1). However, with the configuration in which an abnormality of the cooling system is determined based on the detection values of the temperature sensors, it cannot be identified if the temperature rise of power control elements results from: an increase in amount of heat generation of the power control element caused by a flow of overcurrent; a reduction in flow rate caused by entrance of air or a foreign substance into the flow channel; or a malfunction of water pump 104. Therefore, in order to suppress the temperature rise of the power control elements, the load factor of motor-generator MG may be restricted, or water pump 104 may be replaced incorrectly although it is operable normally.

In this respect, the cooling system according to the present embodiment can detect a partial abnormality of the flow channel by determining whether or not an imbalance in flow rate among the plurality of branches has occurred. It is therefore possible to avoid such a problem that the load factor of motor-generator MG is restricted or unnecessary replacement of water pump 104 is performed.

Moreover, since the cause of the partial abnormality can be identified based on the speed of water pump 104 and cooling water temperature TW when the partial abnormality is detected, the partial abnormality can be solved by executing control for removing that cause.

Exemplary Modification

Although the cooling system according to the present embodiment is configured such that flow rates Fa, Fb and Fc in plurality of branches B1 to B3 are detected by the flow sensors provided for the branches, respectively, it may be configured such that flow rates Fa, Fb and Fc are presumed. As the method of presuming the flow rates, in the cooling system shown in FIG. 2, for example, control device 30 can cause the power control elements in inverter 14 to temporarily generate heat for flow rate presumption under the situation where the condition that another driving instruction is not issued to PCU 40 is satisfied, and can presume the flow rates based on the degree by which the power control elements are cooled thereafter. This allows the flow rates to be detected accurately without providing a flow sensor for each branch.

Diagnostic processing for the cooling system according to an exemplary modification of the embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 is a waveform diagram for illustrating diagnostic timing of the cooling system according to the present exemplary modification.

Referring to FIGS. 1 and 6, when a starting instruction is given by a driver with a start button of the vehicle or the like, the vehicle completes self-check of ECU, for example, to assume a ReadyON state. Thereafter, in the state where the vehicle is set at a parking range and is stopped from time t1 to t2, control device 30 outputs a torque command to inverter 14 for a short time. This torque command is smaller than a torque command during running at and after time t3. Therefore, when the vehicle is set at the parking range and the accelerator pedal is not depressed, torque that causes the vehicle to start to move is not produced.

It is noted that since this torque command for a short time is to cause the power control elements of the inverter to generate heat, it may not produce torque. For example, it may control inverter 14 to flow only a d-axis current of the inverter and not to flow a q-axis current so as not to produce torque.

When a diagnosis of the operating condition of water pump 104 is completed by time t3 and it is confirmed that the operating condition is normal, a torque command is issued in response to an instruction of acceleration/deceleration from the accelerator pedal or the like as shown at time t3 to t4, so that a transition is made to the state where the vehicle can run. It is noted that the point of time t3 may be defined as the ReadyON state.

FIG. 7 is a flowchart for illustrating control of diagnostic timing of the cooling system shown in FIG. 6. When a start switch that activates the vehicular system is set at the ON state, the processing of this flowchart is invoked from a main routine and executed.

Referring to FIGS. 6 and 7, the presence/absence of a charging/discharging operation from battery B using inverter 14 is determined in step S10. In the absence of a charging/discharging operation, the processing advances to step S20, where a diagnosis of the cooling system is performed. An environment with less noise suitable for diagnosing cooling system 104 is thereby ensured. In the presence of a charging/discharging operation in step S10, for example, in the case where the accelerator pedal is depressed immediately, control is returned to the main routine in step S60 for waiting for a next opportunity without diagnosing the cooling system.

It is noted that, in order to give priority to a diagnosis of the cooling system, it may be configured such that the shift position after the start switch may be prohibited from moving from the parking position or input of the accelerator pedal is not accepted until a diagnosis of the cooling system is completed.

In step S20, the power control elements of inverter 14 are caused to generate heat for a short time, and flow rate Ft of flow channel 116 and flow rates Fa, Fb and Fc of branches B1 to B3 are detected based on the degree by which the power control elements are cooled thereafter. It can be diagnosed whether an imbalance among the flow rates has occurred based on detected flow rates Fa, Fc and Fc.

It is determined in step S30 whether or not the cooling system is normal. The processing in step S30 is executed in accordance with the flowcharts of FIGS. 4 and 5. When the cooling system is determined as being normal, the processing advances to step S40, where the charging/discharging operation from battery B using inverter 14 is permitted. The vehicle is thereby allowed to run. It is noted that the detected amount of cooling water may be fed back for use in pump control. On the other hand, when the cooling system is determined in step S30 as not being normal, that is, when an abnormality of the cooling system is finalized, an alarm display is made on the display device, the warning lamp or the like.

When the processing in step S40 or S50 terminates, the control is transferred to the main routine in step S60.

FIG. 8 is a flowchart for illustrating flow-rate detection processing for use in diagnosing the cooling system in step S20 of FIG. 7. The processing of this flowchart is invoked from the processing of the flowchart of FIG. 7 which is the main routine, and executed. Moreover, the processing of this flowchart is executed in parallel for flow channel 116 and branches B1 to B3.

Referring to FIG. 8, the processing of this flowchart is started based on an operation instructing the vehicular system activation or the vehicular system termination. First, control device 30 in step S21 determines whether or not the condition that the shift range is set at the P (parking) range and the accelerator pedal is not being operated (OFF state) is met. While this condition is not met, the processing advances to step S37, and the control is transferred to the main routine. It is noted that, since some hybrid vehicles apply electric power to the inverter of the motor for starting the engine when the amount of power stored in a battery has been lowered, the condition that the amount of power stored in the battery has not been lowered may be added.

When the condition in step S21 is met, the processing advances to step S22, where water temperature Tw at that time is stored as a value Tw0, and an inverter element temperature Ti is stored as a value Ti0.

Then, in step S23, a command torque is determined from a water temperature-command torque map.

FIG. 9 is a diagram showing an example of the water temperature-command torque map referred to in step S23 of FIG. 8. In the example of map shown in FIG. 9, the command torque is set to decrease as the water temperature rises.

Referring again to FIG. 8, in step S24 following step S23, control device 30 gives a command torque determined based on the water temperature to inverter 14 (torque ON). In step S25, the command torque is returned to zero (torque OFF). From the foregoing, the power control elements in the inverter generate heat for a short time as shown at time t1 to time t2 in FIG. 3.

In step S25, control device 30 returns the command torque to zero, and simultaneously stores the temperature of the power control elements in the inverter at that time as a peak temperature Ti1 and stores the time at that time as t1.

FIG. 10 is a diagram for illustrating measurements of temperature drop rate. Referring to FIGS. 8 and 10, the temperature of the power control elements in the inverter starts to rise at time t0 in response to having set the torque command to the inverter at the ON state. The element temperature keeps rising until the torque command to the inverter is set at the OFF state. At time t1 corresponding to having set the torque command to the inverter at the OFF state, the element temperature takes peak value Ti1. This peak value Ti1 and time t1 at that time are recorded on an internal memory of control device 30 or the like during the processing in step S25.

Then, in step S26, a difference value ΔTi01 between peak temperature Ti1 and current inverter element temperature Ti0 is calculated based on an expression (1) below.

ΔTi01=Ti1−Ti0   (1)

Then, in step S27, a specified number of times m is set, and further, a counter is initialized. The counter value n is set at “2”.

The processing from step S28 to step S34 is repeatedly performed based on counter value n.

First, control device 30 in step S28 determines a calculation temperature at which the temperature drop rate of the power control elements of the inverter is calculated. Representing the difference in calculation temperature at which the temperature drop rate of the power control elements of the inverter corresponding to counter value n is calculated by ΔTi1n, an expression (2) below holds.

ΔTi1n=ΔTi01*(n−1)/n   (2)

For example, when n=2, ΔTi12=ΔTi01*½ holds, so that a first measurement shall be performed when the temperature difference is reduced to half. When n=3, a measurement shall be performed when the temperature difference is reduced to one third.

Then, it is determined in step S29 whether or not the current temperature has dropped to temperature Tin expressed by an expression (3) below.

Tin=Ti1−ΔTi1n   (3)

In step S29, when temperature differences ATi12, ATi13 and ATi14 calculated in step S28 drop from peak value Ti1, times t2, t3 and t4 are measured, respectively. Times t2 and t3 can be, for example, times at which the temperature differences become ½ and ⅓ of ATi01, respectively. Although not shown in the flowchart of FIG. 8, a time at which the temperature becomes slightly higher than initial temperature TiO (e.g., +2° C.) like time t4 of FIG. 10 can also be a point of measurement.

Based on a measured time to and stored time t1, time difference Δt1n from time t1 is calculated in step S30. As shown in FIG. 10, time differences Δt12, Δt13 and Δt14 corresponding to temperature differences ATi12, ATi13 and ATi14, respectively, are calculated. The calculated values are recorded on the internal memory of control device 30, for example.

Next, in step S31, the flow rate is calculated from temperature difference ΔTin, time difference Δtin and the drop rate-flow rate map.

FIG. 11 is a diagram showing an example of drop rate-flow rate map. Since the drop rate-flow rate map of FIG. 11 differs among vehicular cooling systems, values experimentally calculated beforehand are used. It is noted that the vehicle itself may acquire data when the water pump is normal immediately after the shipment from the factory and/or an inspection, and this data may be set as a reference value. A calculated flow rate Qn is stored in step S31.

Then, it is determined in step S32 again whether or not the condition in step S21 is continued. This condition is that the shift range is set at the P (parking) range and the accelerator pedal is not being operated (OFF state)

When this condition is no longer met, the processing advances to step S35, where the flow rate is calculated based on results of measurements having been obtained so far. On the other hand, when this condition is still met, the processing advances to step S33, where acquisition of measured data is performed for further improving the accuracy of detected flow rate.

In step S33, counter value n of the counter set in step S27 is incremented by 1. Then, it is determined in step S24 whether or not the counter value is smaller than measured number of times m set in step S27. When n<m holds, the processing of and after step S28 is repeated again, and acquisition of a data pair of time difference Atln and temperature difference ΔTin is continued.

When n is equal to m in step S34 and measurements by specified number of measurement times m are completed, the processing advances to step S35.

In step S35, an average value Qout of flow rates Qj (j=2, . . . m) for the measured number of times is calculated. Then, it is determined in step S36 whether or not the cooling system is normal by execution of the processing in the flowcharts of FIGS. 4 and 5 based on the flow rates detected for flow channel 116 and branches B1 to B3, respectively. In step S37 following step S36, the control is transferred to the flowchart of FIG. 7 which is the main routine.

According to the present exemplary modification, a correct flow rate of coolant medium can be detected, which enables an abnormality of the cooling system to be determined correctly. More specifically, by detecting the drop rate of the inverter element temperature, the amount of cooling water is known from the map showing the relationship between “the drop rate and the flow rate”, without adding a new flow sensor.

Moreover, by performing a pump diagnosis before the start or after the end of running, or in the case of a hybrid vehicle, at the time of engine stop and vehicle stop, a disturbance that would cause the inverter element temperature to rise is removed, which enables correct flow rate detection.

Furthermore, by changing the magnitude of inverter command torque based on the cooling water temperature, the inverter elements can be warmed as a heat source while avoiding damage to the inverter elements.

In addition, by measuring the drop rate several times, the flow rate of cooling water can be calculated accurately from the map showing the relationship between “the drop rate and the flow rate.” In this case, even when running is started or the engine is started (some hybrid vehicles use the inverter of the motor for starting the engine) before measurements are made by the specified number of times, the amount of cooling water can be calculated from the drop rate having been measured so far.

It is noted that although the present embodiment has illustrated the electric vehicle as an example of a vehicle equipped with the cooling system, application of the present invention is not limited to such an example. That is, the present invention is also applicable to any hybrid vehicle with an internal combustion engine used in combination or any fuel-cell vehicle that is equipped with the cooling system.

It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the claims not by the description above, and is intended to include any modification within the meaning and scope equivalent to the terms of the claims.

INDUSTRIAL APPLICABILITY

The present invention is applicable to a vehicle equipped with a cooling system.

REFERENCE SIGNS LIST

10 voltage sensor; 12 voltage converter; 13 voltage sensor; 14 inverter; 15 U-phase arm; 16 V-phase arm; 17 W-phase arm; 24 current sensor; 30 control device; 100 vehicle; 102 radiator; 104 water pump; 106 reservoir tank; 108, 110, 112 temperature sensor; 111 accelerator sensor; 113 shift position sensor; 114 speed sensor; 116, 122 flow channel; 120 cooling water inlet; 124 cooling water outlet; 131 to 133 flow sensor; 400 power element substrate; B battery; B1 to B3 branch; C0, C1 smoothing capacitor; D1 to D8 diode; L1 reactor; MG motor-generator; Q1 to Q8 IGBT element; SMRB, SMRG system main relay. 

1. A cooling system for cooling a heat source, comprising: a flow channel through which liquid medium cooling said heat source is circulated; and a pump provided on said flow channel for circulating said liquid medium, said flow channel including a plurality of branches arranged between an upstream side and a downstream side of said heat source in parallel to a distribution direction of said liquid medium, said cooling system further comprising a control device for detecting an abnormality occurred in any of said plurality of branches by detecting an imbalance among flow rates of said liquid medium flowing through said plurality of branches, respectively, and for diagnosing a cause of occurrence of said abnormality based on the state of said cooling system when the imbalance among the flow rates of said liquid medium is detected.
 2. The cooling system according to claim 1, wherein said control device diagnoses a cause of occurrence of said abnormality at least based on the speed of said pump when the imbalance among the flow rates of said liquid medium is detected.
 3. The cooling system according to claim 2, further comprising a speed sensor for detecting the speed of said pump, wherein in the case where the imbalance among the flow rates of said liquid medium is detected, said control device diagnoses that air has entered said flow channel when a first condition that a detection value of said speed sensor obtained when said pump is driven is higher than a control target value is met.
 4. The cooling system according to claim 3, further comprising a temperature sensor for detecting the temperature of said liquid medium, wherein in the case where said first condition is not met, said control device determines whether or not a second condition that a detection value of said temperature sensor is lower than a predetermined threshold value is met, and when said second condition is met, said control device diagnoses that said flow channel is frozen.
 5. The cooling system according to claim 4, wherein in the case where said second condition is met, said control device determines whether or not a flow rate of said flow channel falls within a control range, and when a third condition that the flow rate of said flow channel falls within said control range is met, said control device diagnoses that any of said plurality of branches is frozen.
 6. The cooling system according to claim 3, wherein in the case where said first condition is not met, said control device diagnoses that a foreign substance has entered any of said plurality of branches when said second condition is not met.
 7. The cooling system according to claim 3, wherein in the case where it is diagnosed that one of air and a foreign substance has entered any of said plurality of branches, said control device temporarily increases the speed of said pump.
 8. The cooling system according to claim 5, wherein in the case where it is diagnosed that any of said plurality of branches is frozen, said control device temporarily increases the amount of heat generation of a heat source corresponding to a branch diagnosed as frozen.
 9. The cooling system according to claim 1, wherein said heat source is a driving device having a motor and an inverter driving said motor, said cooling system further comprising an element temperature sensor detecting the temperature of a power control element in said inverter, wherein under a situation where a condition that another driving instruction is not issued to said inverter is satisfied, said control device temporarily causes the power control element in said inverter to generate heat and then reduces heat generation of said power control element to presume the flow rates of said plurality of branches depending on the degree of drop of a detection value of said element temperature sensor, and detects an imbalance among the flow rates of said liquid medium based on presumed values of the flow rates of said plurality of branches.
 10. The cooling system according to claim 1, wherein said plurality of branches are configured to have an equal flow rate.
 11. A vehicle comprising: a driving device using a motor (MG) as a drive source; and a cooling system for cooling said driving device, said cooling system including a flow channel through which liquid medium cooling said driving device is circulated, and a pump provided on said flow channel for circulating said liquid medium, said flow channel including a plurality of branches arranged between an upstream side and a downstream side of said heat source in parallel to a distribution direction of said liquid medium and configured to have an equal flow channel area, said vehicle further comprising a control device for detecting an abnormality occurred in system any of said plurality of branches by detecting an imbalance among flow rates of said liquid medium flowing through said plurality of branches, respectively, and for diagnosing a cause of occurrence of said abnormality based on the state of said cooling system when the imbalance among the flow rates of said liquid medium is detected. 